It has been proposed in the past to provide various elastic or resilient means on the sole of a shoe to provide a degree "springiness" under the foot of the wearer of the shoes. However, such prior art spring devices are characterized by many limitations whether they are separately attached to the soles of the shoes or whether they are built into the shoe sole. Obviously, to build such spring devices into the shoe adds considerably to the manufacturing cost of the shoe and furthermore limits the use of the shoe for a single purpose. Where spring devices are separately attached to a shoe, some, modification of the shoe sole is still necessary and, in addition, are limited in durability, performance and effectiveness.
The following prior art patents are representative of spring devices for use on shoes all of which are clearly distinguishable from that of applicant's invention: U.S. Pat. Nos. 1,571,073, Tapling; 4,030,213, Daswick; and 3,668,792, York.
The York patent refers to an athletic safety shoe provided with a safety sole having a grooved track configured to slidably receive a rib with a pressure piece engaged with the rib biases by a spring into frictional engagement with the rib. The Daswick patent is directed to a sporting shoe having a relatively thick sole in which a plurality of springs are embedded to enhance the compressive and expansive ability of the resilient sole members 15, 16. The Tapling patent relates to an exercising device which include a sole plate 1 arranged to be attached to a shoe and having a runner formed of a steel strip 2 configured in a arcuate fashion throughout and attached to the sole plate 1 adjustably so that the wearer of the shoes may perform a jumping or leaping action.